Most aluminum alloys contain several alloying elements to enhance the properties of the finished product. Such alloying elements include but are not limited to copper, magnesium, manganese, silicon, chromium, strontium, phosphorous, zirconium, zinc, and iron. These elements are added as pure metal, powders, or master alloys. The form of the addition is dictated by cost of the raw material, consistency, influence on melt quality, and dissolution rate.
Master alloys provide the desired alloying elements in more concentrated form than the concentration of such elements in the final aluminum base product. See U.S. Pat. No. 3,591,369 issued Jul. 6, 1971 to Tuthill, which is incorporated herein by reference.
Conventional aluminum master alloys are usually binary systems composed of two components only, such as aluminum and manganese as disclosed in the Tuthill patent. Some higher component master alloys are disclosed in the art. See U.S. Pat. No. 4,353,865 issued Oct. 12, 1982 to Petrus, U.S. Pat. No. 4,185,999 issued Jan. 29, 1982 to Seese et al., U.S. Pat. No. 4,119,457 issued Oct. 10, 1978 to Perfect, U.S. Pat. No. 4,104,059 issued Aug. 1, 1978 to Perfect, U.S. Pat. No. 4,062,677 issued Dec. 13, 1977 to Perfect, and U.S. Pat. No. 3,725,054 issued Apr. 3, 1973 to Perfect, all of which are incorporated herein by reference. However, these alloys have limited purposes and are designed to take advantage of available and less costly raw material alloy mixtures, such as strontium/silicon or ferro-silicon alloys.
Virtually all of the aluminum alloys encountered today are either ternary, quartenary, or of higher level composition. Thus, the production of commercial aluminum alloys generally involves the addition of pure metals and/or two or more binary master alloy hardeners to achieve the proper chemistry in the base heat. These multiple additions result in longer holding times in the furnace than desirable and may significantly reduce the recovery of critical alloying elements present in the final base alloy. In addition, purchasers of the binary master alloy hardeners obtain greater amounts of the aluminum base than they usually desire.
Often, a company that produces aluminum base alloys for fabrication into intermediate or final products will recycle production scrap in the process. In some instances, the scrap may be in a form that is readily recycled, but other forms of scrap can cause substantial metal loss if introduced in their original form into melting furnaces. The latter category includes machining chips, foil, and fine wire. These operations require several additions of pure metal or binary master alloy hardeners, which have the disadvantages mentioned above. Also, the addition of scrap to a conventional aluminum melting furnace, when the scrap is in a form with a high surface to volume ratio and has oil, paint, or other contaminants, generates large quantities of oxides. This reduces metal recoveries and requires additional melt treatment. When properly treated and melted, the recovery of both aluminum and alloying elements can be conserved and efficiently utilized.
Thus, there is a significant need for master alloy hardeners that contain concentrated amounts of all of the alloying elements in the proper proportions so that the final aluminum base alloy is obtained after the addition of only one type of master alloy hardener to commercially pure aluminum, recycled aluminum alloy production scrap, or a combination of the two. This would reduce furnace time by eliminating or limiting multiple pure metal and master alloy additions, would improve metal recovery from certain types of scrap, and would allow inventory reduction by providing more concentrated master alloys. The master alloys of the present invention overcome these deficiencies in the art.